⚡ electrical engineering

Microdiversity and Vegetation Influence on Forward Scattering at 60 GHz and 80 GHz

This paper presents an experimental study demonstrating that vegetation and small-scale antenna movements significantly impact forward scattering at 60 GHz and 80 GHz, with the 80 GHz band showing greater sensitivity to micro-movements and resulting in larger received power fluctuations.

Original authors: Radek Zavorka, Ondrej Zeleny, Jiri Blumenstein, Tomas Mikulasek, Rajeev Shukla, Josef Vychodil, Jaroslaw Wojtun, Niraj Narayan, Aniruddha Chandra, Jan M. Kelner, Cezary Ziolkowski, Ales Prokes

Published 2026-03-20

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Radek Zavorka, Ondrej Zeleny, Jiri Blumenstein, Tomas Mikulasek, Rajeev Shukla, Josef Vychodil, Jaroslaw Wojtun, Niraj Narayan, Aniruddha Chandra, Jan M. Kelner, Cezary Ziolkowski, Ales Prokes

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine you are trying to shout a secret message to a friend across a room. Usually, you just shout, and they hear you clearly. But what if you put a giant, leafy potted plant right between you? And what if, while you're shouting, you take a tiny step to the left or right—just a few centimeters?

That is essentially what this paper is about, but instead of shouting, scientists are using invisible radio waves (the kind that power your Wi-Fi and future 5G/6G networks) at very high speeds: 60 GHz and 80 GHz.

Here is the story of their experiment, broken down into simple concepts:

1. The Setup: A Game of "Hide and Seek" with Radio Waves

The researchers set up a controlled experiment in an empty conference room.

The Players: A transmitter (TX) and a receiver (RX) were facing each other, about 4.5 meters apart.
The Obstacle: They placed a potted plant right in the middle, blocking the direct path. Think of the plant as a "traffic jam" for the radio waves.
The Twist: They didn't just leave the equipment still. They put the transmitter and receiver on special sliding tables (like a camera slider) and moved them back and forth by tiny amounts—sometimes just a fraction of a millimeter.

2. The Two Speeds: 60 GHz vs. 80 GHz

They tested two different "frequencies" (or pitches) of radio waves:

60 GHz: This is like a standard high-speed highway. It's fast and widely used.
80 GHz: This is an even faster, super-highway. It's the "E-band," a newer technology being considered for next-gen networks.

The Big Difference: The 80 GHz waves have a shorter "wavelength" (the distance between wave peaks) than the 60 GHz waves. Imagine 60 GHz as a large ocean wave and 80 GHz as a choppy, rapid ripple.

3. What Happened When They Moved? (The "Micro-Movements")

The scientists wanted to see what happens when the antennas move just a tiny bit (micro-shifts).

The 60 GHz Experience: When they moved the antennas slightly, the signal strength changed, but it was relatively stable. It was like walking through a light rain; you get a little wet, but you don't notice a huge difference.
The 80 GHz Experience: When they moved the antennas slightly, the signal strength went wild! It fluctuated wildly.
- The Analogy: Imagine walking through a dense forest with a flashlight. If you move your hand just an inch, the beam might hit a leaf and reflect away, or hit a gap and shine through. Because the 80 GHz waves are so "small" and "choppy," a tiny movement changes exactly which leaves they hit and how they bounce. This caused the signal to jump up and down much more violently than at 60 GHz.

4. The "Plant" Factor

The plant wasn't just a prop; it was the main villain.

Absorption: The water inside the leaves and branches soaked up the radio energy, making the signal weaker (attenuation).
Scattering: The leaves acted like tiny mirrors, bouncing the signal in random directions. This created a "messy" signal where the receiver had to pick up the main signal plus a bunch of echoes.

5. The Main Discovery

The most important takeaway is this: The higher the frequency (80 GHz), the more sensitive the system is to tiny movements.

At 60 GHz, moving the antenna a tiny bit changed the signal strength by less than 1 dB (a very small change).
At 80 GHz, that same tiny movement caused the signal to fluctuate by up to 2 dB or more.

Why does this matter?
If you are building a future network that uses 80 GHz (which promises super-fast internet), you have to be incredibly precise. If a wind blows a tree branch, or if a car drives by and shakes a pole holding an antenna, the 80 GHz signal might flicker or drop out much more easily than a 60 GHz signal.

Summary

Think of the 60 GHz band as a sturdy, wide river that can handle a few pebbles (leaves) and small ripples (movement) without changing its course much. The 80 GHz band is like a delicate stream of water; if you drop a single leaf in it or move a finger near the surface, the whole flow changes direction.

The Conclusion: To make the fastest future networks work, engineers need to design systems that can handle these tiny, chaotic movements, especially when trees and plants are involved. The 80 GHz band is powerful, but it's also much more "jittery" and sensitive to its environment.

1. Problem Statement

As wireless communication networks evolve toward higher frequency bands (millimeter waves, or MMW) for 5G and beyond, understanding signal propagation in real-world environments is critical. Two specific challenges are addressed:

Vegetation Impact: Trees and foliage significantly attenuate signals due to high water content in leaves and branches, causing absorption and scattering. While attenuation at 28 GHz is documented, data on the specific behavior of forward scattering and attenuation at 60 GHz and 80 GHz (E-band) in the presence of vegetation is less explored.
Microdiversity Sensitivity: High-frequency signals have short wavelengths, making them highly sensitive to small-scale antenna movements (micro-shifts). The paper investigates how minute positional changes (fractions to multiples of a wavelength) affect the Channel Impulse Response (CIR) and received power when a vegetation obstacle is present.

2. Methodology

The authors conducted a controlled measurement campaign in an indoor conference room to simulate a Line-of-Sight (LOS) scenario obstructed by vegetation.

Experimental Setup:
- Frequency Bands: 60 GHz (ISM band) and 80 GHz (E-band, 81–86 GHz).
- Distance: Transmitter (TX) and Receiver (RX) were separated by 4.75 meters.
- Obstacle: A potted plant (approx. 2.8 m tall, 0.8 m diameter) was placed at the midpoint (2.4 m from TX), deliberately obstructing the direct LOS path.
- Antenna Configuration: Horn antennas were mounted on XY tables allowing precise micro-positioning in both horizontal and vertical axes. Heights were set at 1.6 m (60 GHz) and 1.5 m (80 GHz).
- Hardware:
  - Baseband: Xilinx Zynq UltraScale+ RFSoC (ZCU111) generating I/Q components.
  - Waveform: Frequency Modulated Continuous Wave (FMCW) with 2.048 GHz bandwidth and 8 µs sweep duration.
  - Up/Down Conversion: Sivers IMA converters (FC1005V/00 for 60 GHz; FC1003E/03 for 80 GHz).
  - Synchronization: 10 MHz GPS-disciplined oscillator.
Measurement Process:
- The Channel Impulse Response (CIR) was measured for incremental antenna displacements.
- Data was analyzed to extract the Power Delay Profile (PDP).
- Metrics: Received Power (RP) was calculated for three scenarios:
  1. LOS: The dominant first path.
  2. NLOS: All multipath components (MPC) excluding the dominant LOS.
  3. Total: Combined LOS + NLOS.
- Statistical analysis (mean and standard deviation) was performed across different antenna positions to quantify microdiversity effects.

3. Key Contributions

Controlled Vegetation Study: Provided empirical data on signal propagation through a simplified vegetation model (potted plant) specifically at 60 GHz and 80 GHz, isolating the effects of forward scattering.
Micro-movement Analysis: Quantified the sensitivity of MMW channels to sub-wavelength antenna shifts in the presence of foliage, a critical factor for static and quasi-static network planning.
Comparative Frequency Analysis: Directly compared the performance and stability of the 60 GHz band against the 80 GHz E-band under identical environmental conditions.

4. Key Results

Frequency Sensitivity to Micro-movements:
- 80 GHz Band: Exhibited significantly higher sensitivity to antenna positioning. The fluctuation in LOS relative power ranged from 0 dB to -18 dB (a span of 18 dB).
- 60 GHz Band: Showed lower sensitivity, with LOS power fluctuating between -2 dB and -7 dB (a span of 5 dB).
- Conclusion: The 80 GHz band is more than three times more sensitive to micro-shifts than the 60 GHz band due to its shorter wavelength.
Statistical Variance (Standard Deviation):
- The standard deviation ( $\sigma$ ) of received power was consistently higher for 80 GHz across all antenna positions.
- For the combined LOS+NLOS signal, the standard deviation at 80 GHz reached up to ~2 dB (specifically ~1.97 dB in Table III), whereas at 60 GHz it remained below 1 dB (specifically ~0.8 dB).
Vegetation Attenuation:
- The presence of the plant caused significant additional attenuation.
- NLOS Power: When the dominant LOS path was suppressed, the mean received power dropped to approximately -48 dB for 60 GHz and -48.5 dB for 80 GHz.
- The total received power (LOS + NLOS) was approximately 30 dB lower than the free-space path loss would suggest without the plant, highlighting the severe impact of foliage even in a "forward scattering" (obstructed LOS) scenario.
Atmospheric Considerations: The paper notes that while oxygen absorption is high at 60 GHz (~~15 dB/km), it is negligible at 80 GHz (~~0.4 dB/km) over the short 4.75 m test distance, meaning the observed differences are primarily due to scattering and diffraction effects rather than atmospheric absorption.

5. Significance and Implications

Network Design: The findings suggest that systems operating at 80 GHz require much stricter alignment tolerances and potentially more robust beamforming or diversity schemes compared to 60 GHz systems, especially in environments with vegetation.
Microdiversity Utilization: The high sensitivity to micro-movements at 80 GHz implies that even small mechanical vibrations or thermal expansions in antenna mounts could cause significant signal fading. Conversely, this sensitivity could be exploited for high-resolution sensing or micro-diversity techniques if the system can rapidly adapt.
Propagation Modeling: The data provides a benchmark for validating propagation models in MMW bands where vegetation is a factor, moving beyond theoretical path loss models to include scattering effects from foliage.

In summary, the paper demonstrates that while both 60 GHz and 80 GHz are heavily attenuated by vegetation, the 80 GHz band is significantly more volatile regarding small-scale antenna positioning, necessitating careful engineering considerations for deployment in outdoor or semi-outdoor environments containing greenery.